The syrinx is the vocal organ of birds. In oscine songbirds the syrinx includes two independent sound sources, the internal tympaniform membranes, one in each bronchus. Each sound source has its own set of muscles which in turn are controlled by a branch of the hypoglossus nerve. Cutting the left hypoglossus in adult chaffinches and canaries leads to a lasting song loss. Section of the right hypoglossus has little or no effect. Section of the left hypoglossus in young birds, before they have started to develop their song, results in the right hypoglossus assuming a dominant role. The age, experiential, and hormonal conditions which permit this reversal of dominance are now under study. This project also seeks to plot brain areas involved in song control and establish their connectivity. This will be achieved by placing electrolytic lesions in various brain areas, staining for nerve degeneration, and noting effects on song. Experiments with parrots and flycatchers will establish the extent to which hypoglossal dominance may occur in those groups.